1. Field of the Invention
The present invention relates to a process of producing solid manganese dioxide by the oxidation of manganese oxide with a chloric acid solution.
2. Brief Description of the Art
Manganese dioxide (MnO.sub.2) (also known as manganese binoxide, manganese peroxide; manganese superoxide; and black manganese) is a strong oxidizer and is used in the manufacture of manganese steel; in alkaline batteries (dry cells); for making amethyst glass or decolorizing glass; and painting on porcelain, faience, and majolica. It is also used in electrotechnics, pigments, browning gun barrels, drier for paints and varnishes, printing; dyeing textiles; and making potassium permanganate. It is characterized as follows: has a molecular weight of 86.94; when ignited, evolves oxygen and leaves Mn.sub.3 O.sub.4 ; insoluble in water, nitric acid, or cold sulfuric acid; slowly dissolves in cold HCl with evolution of Cl.sub.2 ; in the presence of hydrogen peroxide or oxalic acid, it dissolves in dilute H.sub.2 SO.sub.4 or HNO.sub.3.
Manganese dioxide is a naturally occurring substance; it occurs in nature as the mineral pyrolusite. It is also made artificially by various processes.
U.S. Pat. No. 3,640,683, which issued to Miyazaki et al. on Feb. 8, 1972, teaches several processes for making manganese dioxide:
(1) thermal decomposition of manganese nitrate (MnNO.sub.3) to manganese dioxide and NO gas;
(2) oxidation of manganese hydroxide [Mn(OH).sub.2 ] particles with air or an oxidizing agent or oxygen or ozone to form manganese dioxide;
(3) oxidation of manganese sulfate (MNSO.sub.4) with an oxidizing agent (e.g., chlorate, hypochlorite, permanganate, or peroxide) to form manganese dioxide and by-product salts and gases;
(4) disproportion of a manganese suboxide (Mn.sub.2 O.sub.3) with sulfuric acid to form manganese dioxide and a manganese sulfate by-product;
(5) thermal decomposition of manganese chloride; and
(6) roasting a naturally occurring, but crude, manganese dioxide-containing ore with air or oxygen; then reacting the roasted ore with a hot aqueous solution of chlorate salt and sulfuric acid; separating the formed needle-like manganese dioxide particles from the hot aqueous solution and then washing the separated manganese dioxide with water.
U.S. Pat. No. 4,402,931, which issued to Tanabe et at. on Sep. 6, 1983, teaches a process of producing manganese dioxide by (1) heating and decomposing a solution of ammonio complex of manganese (manganese ammonium carbamate) at a temperature of 68.degree.-80.degree. C.; (2) then optionally roasting the resulting manganese carbonate in air containing 15-85% steam; (3) roasting the manganese carbonate at a temperature of 275.degree.-375.degree. C. in oxygen containing 15-85% steam; and (4) treating the resulting manganese dioxide by heating it in either (a) a diluted sulfuric acid, (b) a solution of sulfuric acid and chlorate, or (c) a solution of sulfuric acid, manganese carbonate and chlorate.
In the commercial process for producing manganese dioxide by chemical oxidation that involves an acidic solution made by sulfuric acid and sodium chlorate salt, the oxidation reaction consumes chlorate and releases chlorine (Cl.sub.2) and chlorine dioxide (ClO.sub.2) gases as well as producing sodium ions, sulfate ions, sulfuric acid, and chlorate ions as by-products which must be purged from the system. The chlorine (Cl.sub.2) and chlorine dioxide (ClO.sub.2) gases may be hazardous if large concentrations are formed. These gases and the by-products require neutralization, which may involved large quantities of a base. Accordingly, such processes have important commercial limitations.
U.S. patent application Ser. No. 07/987,503, which was filed Dec. 7, 1992 with Leslie Ward and David Cawlfield as the named inventors and has been allowed as U.S. Pat. No. 5,279,743, teaches a process of separating zinc and manganese oxide by (1) reacting said oxide mixture with a chloric acid solution to form a mixture having a solid phase containing manganese dioxide and a liquid phase containing chloric acid solution and dissolved zinc ions contained therein and (2) then separating the solid and liquid phases. This reference further teaches mixing the separated solid phase with a second chloric acid solution to dissolve remaining zinc oxide in the manganese dioxide and then separating that second chloric acid solution containing additional zinc ions from a substantially pure solid manganese dioxide product.
While the teachings of U.S. patent application Ser. No. 07/987,503, now U.S. Pat. No. 5,279,743, represent a significant commercial advance over the preexisting oxidation routes for making manganese dioxide, the problem of recovering the valuable chloric acid after separation of the solid manganese dioxide exists. The present invention is a solution to that problem. Furthermore, the invention of patent application Ser. No. 07/987,503, now U.S. Pat. No. 5,279,743, is limited to a process of separating zinc and manganese oxides with chloric acid. It has now been found that an extension of that invention is also acceptable to producing manganese dioxide from quantities of manganese oxide not contaminated with zinc oxide and also allows for the recovery of valuable chloric acid.